Treating vegetable fibrous material with chlorine gas



Jan. 10, 1956 F. G. 1.. Beam 2,730,426

TREATING VEGETABLE FIBROUS MATERIAL WITH CHLORINE GAS Filed June 20, 1951 3 Sheets-Sheet l INVENTOR FREDERICK G.L. BECKER,DECEASED,

BY E.GOULDING AND D. JOHN,EXECUTOR$ Jan. 10, 1956 BECKER 2,730,426

TREATING VEGETABLE FIBROUS MATERIAL WITH CHLORINE GAS Filed June 20, 1951 3 Sheets-Sheet 2 INVENTOR FREDERICK e.| BECKER, DECEASED,

BY E. GOULDING AND D. JOHN,EXECUTORS Jan. 10, 1956 F. G. BECKER 2,730,426

TREATING VEGETABLE FIBROUS MATERIAL WITH CHLORINE GAS Filed June 20, 1951 3 Sheets-Sheet 3 l I i i 127 f l 1 +14% v ":r' W

2 a i a Z iP $M za 2/ 52 INVENTOR FREDERICK G. L. BECKER, DECEASED BY E. GOULDING AND D. JOHN, EXECUTbRS 7 TREATING VEGETABLE FIBROUS MATERIAL WITH CHLORINE GAS Frederick George Lucas Becker, deceased, late of Hatch End, England, by Edward Goulding and Dorothy John, executors, London, England, assignors to Cellulose Development Corporation Limited, Hatch End, England, a British company Application June 20, 1951, Serial No. 232,648

2 Claims. (Cl. 8-105) Many proposals have been made for treating fibrous materials with chlorine, and various types of apparatus have been prepared and installed for treating moist or liquid suspended fibrous material with chlorine at fibre concentrations ranging from 1% to 40% by weight of the mass.

It is well known in the pulp and paper industry to treat fibrous materials in diluted suspensions with chlorine, and two methods are commonly adopted. Chlorine may be added to the pulp suspension in the form of chlorine water, previously prepared or injected'into the pulp suspension in the form of chlorine, gas. Normally, in the pulp production industry, fibrous material, previously cooked by known methods such as the soda, sulphate or sulphite processes, while in liquidsuspension of 35% fibre concentration is treated with chlorine in towers.

It is found diificult in commercial practice when operating in this manner, completely to chlorinate pulp having a high chlorine demand in one stage. If too much chlorine gas is injected into the pulp suspension the chlorine may be liberated and escape from the top of the tower or chest, in which the chlorination is carried out. A characteristic of the chlorination process .is that 85-90% of the chlorine consumed is normally absorbed very quickly (in say 10 to -15 minutes) by the fibres, whereas the absorption of the remaining 10% to 15% takes much longer. Chlorination is frequently carried out in several stages. This is also due to the'fact that in dilute suspensions due to the small degree of solubility of chlorine in water, it is difiicult to add in any one stage more than 3% to 5% chlorine on the weight of the pulp. When chlorinating in this fashion therefore, it is normally necessary to continually test the different batches of fibrous material, and to endeavour so to regulate the chlorine dose that the right amount is added at each stage.

Another disadvantage of chlorinating pulp in a dilute condition is that acid may have to be artificially added to the pulp to raise the acidity of the dilute suspension, as it is found in practice in accordance with this invention that unless the pulp has an aciidty of -40 grammes per litre during chlorination, the strength of the resulting pulp may be adversely afiected.

It has also been proposed by Umberto Pomilio in various patents such as British Patent No. 415,224 to treat fibrous materials at high fibre concentrationviz. 25-40% as they continuously descend through a tower, the gas being blown into the pulp at about /3 of the distance from the top of the tower.

The fibrous material is extracted from the base of the tower by extraction arms-and dropped to a dilution chest beneath the tower.

By this continuous method good pulps can be produced and there is no risk of chlorine escaping from the top of the tower because the pulp continually passing down the upper'part of the tower absorbs any excess which rises above the chlorine inlets. The highconcentration also ensures a. high concentration of HCl in the chlorinated pulp, thus inhibiting-damage to the fibre.

nited [rates Patent 0 The elongated shape of the tower tends to make uniform distribution of the chlorine through the mass, somewhat diflicult and considerable volumes of air require to be blown in with the chlorine to ensure efiicient distribution and to cool the pulp mass. A convenient and effective method of introducing the chlorine and air is by pipes which extend down the centre of the tower. These pipes tend to create a continuous hole in the high density pulp in the lower part of the tower down which hole the surplus gas'and air escapes from the pulp and accumulates above the level-of the liquid in the chest and chlorine extraction fans have hitherto been fitted to extract the surplus gas and air mixture and arrangements have had to be made to dispose of it.

The extractor gear used in the type of tower referred to also is very expensive, as it has to be specially constructed of chlorine resisting material.

An object of the present invention is to overcome such disadvantages.

According to this invention, a method of treating moist fibrous materials with a reacting gas in a vertical tower having a gas outlet at the top consists in introducing into the top of the tower or chest a continuous supply of moist fibrous material, diluting the material with water during its travel through the tower or chest, extracting the material through an outlet at the bottom of the tower or chest, and simultaneously introducing the treating gas into the tower or chest between said top and bottom outlets so that any undissolved or uncombined gas must travel upwards through the descending mass of untreated fibrous material and whereby the fibre concentrations of the mixture is reduced during the passage of the material through the tower. It will be appreciated that by adopting this method the only outlet for undischarged gas is through the fibre concentrate at higher concentration. The chlorination reaction can be observed through windows in the tower, and by controlling the amount of chlorine added, so as to maintain the colour change in the tower at a constant level above the chlorine inlets, even and full chlorination can be ensured with no risk or escapes of gas and without the necessity of continually testing the fibrous material to determine its potential chlorine demand.

In one method of treating fibrous materials as set out above the fibre concentrate in the first step may be from about 10% to 40% and in the second step is below 10%, normally atabout 2% to 5% concentration. The two steps are preferably carried out in separate towers.

The amount of chlorine employed in the first step may be such as to produce an acidity of from 10 to 40 grammes HCl per litre of water present, While the acidity employed in the second step may still be retained at between 10-40 grammes per litre by using for the dilution of the pulp acid wash water recirculated from the chlorinated pulp wash filter which is used in a subsidiary stage of the process.

The time during which the material is subjected to chlorine in the first stage may be quite short (say about 10 to 45 minutes) due to the rapid rate at which the chlorine is absorbed at high density. If sufiicient chlorine is added, about to of the total chlorine demand of the pulp is normally absorbed at this stage. The second step at more dilute consistency-normally at 2 to 5%may last up to one hour and during this longer period at dilute consistency, the proportion of chlorine not absorbed during the more rapid high density stage will be consumed. During this stage, if the percentage of chlorine remaining to be consumed is small, the maintenance of the acidity of the stock between 10 and 40 grammes per litre may not be of major importance.

When passing from the high to the low density stages, fibre and liquid are subjected to vigorous agitation.

The above method is particularly applicable to a continuous process as distinct from a batch process, and for this purpose the pulp is continuously passed through successive reaction towers.

An apparatus for carrying out the above method consists essentially in means for initially consolidating the moisture containing fibres so that the pulp may have a consistency of 10% to 40% fibre content, one or more upright tubular towers having a smooth chlorine resistant lining, which tower or towers at their lower ends are supported on and communicate with a chest, means for intro ducing chlorine gas into the towers, means for introducing water at a controlled rate into the chest, and an agitator in the chest for mixing the water with the pulp with or without means for introducing chlorine into the chest and means for continuously withdrawing the treated pulp from the chest.

The following is a description of two alternative torms of reaction towers and an apparatus which first renders the fibrous material suitable for feeding to the tower, reference being made to the accompanying drawings in which:

Fi ure l is side elevation of the apparatus for rendering the fibrous material suitable for treatment with chlorine;

Figure 2 is a side elevation of a reaction tower and a section through the chest on which the reaction tower rests;

Figure 3 is a plan View of the arrangement shown in Figure 2;

Figure 4 is an elevation of the lower end of an alternative form. of chlorine reaction tower; and of the chest and;

Figure 5 is a plan view of the arrangement shown in Figure 4-.

The fibrous raw material is first treated in known manner in a digestor which removes the pithy material etc, and after the digested material has been washed it is fed into a vacuum filter diagrammatically illustrated in Figure l and from thence passes to a screw press 11 where it is consolidated and fed by a screw conveyor -12 into an opening machine 13. The resulting pulp then has a fibre concentration of about 10% to the opening machine loosens the fibre into a fluffy state, and it passes out through a delivery conduit 14 whence it is directed under the action of gravity into the open ends of two upright towers 15. The towers may be of circular cross-section and lined with smooth chlorine resisting material such as chemical stoneware, glass or plastic. also be used, but it is generally found simpler to construct the tower of stoneware sections. Alternatively, the towers may comprise rubber lined steel tube or tubes lined with chlorine resisting plastic material.

The diameter of the vertical tubes is limited by the capacity of the chlorine gas for penetrating the mass.

A very suitable diameter has been found to be 21", but larger or smaller diameters up to 36" can be employed. The height of the towers may be from 10 to feet which is sufficient to allow for a time of travel through the tower of from ten to sixty minutes.

A pipe 16 is arranged to pass down the centre of each tube and the portion of the pipe within the tower is perforated. Chlorine is fed to this pipe and is also blown into the tower through a number of inlets 17 disposed around the circumference of the tower at different levels. The extent to which the chlorine rises up the tower can be seen through a number of glass windows 18 provided for the purpose. The circular section of thetubes enables the penetration of the chlorine to be accurately and evenly controlled. The two tubular towers sit on a chest 19 which may be of circular section, as shown in Figure 3. The chest is constructed of a chlorine resisting material, such as rubber-lined steel or tile-lined concrete. The chest 19 is also provided with a chlorine inlet 20 and with inlets '21 Tile lined concrete tube can for dilution water. The towers are open at their bottom so that the materials descend through the tower and completely fills the chest. The chest is provided at the bottom with an outlet connection 22 and an outlet 23 for withdrawing sludge. Mounted above the chest is a motor 24 which drives an upright shaft 25 through gearing 26, which shaft projects into the chest. The shaft is provided with a number of blades 27 by which the material within the chest is vigorously stirred. The rate of descent of the material through the towers is controlled by a valve (not shown) associated with the outlet 22 from the chest.

In practice, it is found that a suitable rate of descent of the material in the tower for the first step in the process is about a quarter to one foot per minute. The height of the tower and the speed of the traverse is so selected as to allow about 10 to 45 minutes for the high density chlorine reaction to take place. The diluted pulp after being withdrawn may pass with or without the assistance of a pump through a further chest or up a large diameter retention tower before being washed and thickened and subjected to the usual alkaline treatment.

The power required for driving the agitator within the chest will depend on the consistency of the diluted pulp. if the pulp thickens or becomes more dilute, more or less amperes are consumed by the motor driving the agitator. This variation in amperes is arranged automatically to operate a valve which controls the rate of introduction of the diluting Water whereby the consistency of the pulp in the chest is automatically controlled. The consistency of the pulp in the chest can also be manually controlled. In that case the diluting valve is controlled by an operator who has in front of him an ammeter connected to the agitator drive and motor and he adjusts the flow of diluting liquid according to the ammeter reading. The advantages of this step of the procedure are as follows. First, it is possible to add any desired quantity of chlorine to the pulp in a single operation. Pulps having a very high chlorine demand (say from 6 to 30% on the weight of the pulp may receive a treatment with gaseous chlorine lasting only a few minutes in the tubular sections, thus avoiding any heat damage to the fibres. Normally, about of the chlorine required is absorbed in a very few minutes at a high density, but the remaining 10% takes longer, and any chlorine remaining unabsorbed in the pulp in the tubular section can be absorbed in the longer period available in the retention tower or chest at lower dilution.

Where the chlorine demand is small, the whole of the chlorine required can be added to the dilute material and any surplus gas rising up through the tubes will be absorbed by the descending pulp. in this way, therefore, it is possible to chlorinate the pulp at any desired consistency from 1 up to 40% and with any desired percentage of chlorine up to the full chlorine demand of the material.

The method may also be applied to the treatment of fibrous materials with other gases such as chlorine dioxide S02, etc.

In the alternative form of construction shown in Figures 4 and 5, the two towers 15 sit on a concrete chest 28 which is provided with a conical bottom 29 having a bearing 30 through which the agitator shaft 25 extends. The shaft is driven by a motor 124 and gearing 26 disposed beneath the bottom of the chest. The outlet 22 from the chest communicates with the inlet of a pump 23. The outlet of the pump communicates with an upright pipe 24 or with a vertical tower, which will allow additional retention time if required to complete the chlorination and which feeds the material to the next stage of treatment which may be a washing treatment and the acid water from the treating vessel may be fed back to the inlet -21 thus maintaining the required acidity of the chlorine treatment in the chest.

The normal operation is that the digested straw pulp comes down the tower at about 30% consistency looking like damp tobacco. This collects on top of the chest. The dilution water is injected where shown below this layer of thick pulp, and the material is continuously eX- tracted from the chest at a controlled rate through a valve (which is not shown).

The water normally does not rise up in the tubular part of the tower because the density is so controlled in the chest that this does not occur. The concentration of the greater part of the content of the chest would be maintained at a steady consistency of around 3% (i. e. 2 t 5%). The chest itself will give a certain extra time for the absorption of small quantities of free chlorine, but if more time is required to complete the reaction, the pipe 24 may be replaced by an additional tower which in that case should be 6-8 feet or more in diameter. In this way the chlorination can be so regulated that the pulp stays only a short time in contact with the chlorine, at high density, and a much longer time in contact with the chlorine at low density.

Normally, materials are being treated with a high chlorine demand (say, 620%) and in that case add all the chlorine in the tubular part, and sufiicient surplus chlorine is carried down between the fibres to give an addi tional mild chlorination effect in the dilute stage.

When chlorinating a material with a very small chlorine demand, say l3%, it might be diflicult to get even distribution in the high density tubes, and the logical place to add thesmall quantity of chlorine would be in the chest.

What is claimed is:

1. A method of treating vegetable fibre pulp with chlorine gas in two stages in which the fibre concentration of the pulp is reduced in the second stage, characterised in that during the first stage the reaction with the gas is carried out on the pulp in continuous, uninterrupted form having a fibre concentration from between 10% to for a period of between 10 to minutes, whereafter the pulp without modification passes directly to a second stage zone where it is diluted so that its fibre concentration is below 10% and where continued reaction takes place for a prolonged period up to one hour, and the method being further characterized in that the quantity of gas introduced is such that during at least the first stage the pulp has an acidity from 10 to 40 grms. of hydrochloric acid per litre.

2. The method of claim 1 wherein gaseous chlorine is added to the diluted pulp in the second stage zone.

References Cited in the file of this patent UNITED STATES PATENTS 401,610 Tompkins Apr. 16, 1889 514,374 Meurer Feb. 6, 1894 620,243 Lyman Feb. 28, 1899 1,500,378 Drewsen July 8, 1924 1,548,477 Morterud Aug. 4, 1925 1,843,465 Traquair Feb. 2, 1932 1,864,220 Rutr June 21, 1932 1,895,266 Morterud Jan. 24, 1933 1,907,548 John May 9, 1933 1,911,608 Davis et a1 May 30, 1933 1,942,622 Traquair Jan. 9, 1934 1,991,244 Roza Feb. 12, 1935 2,059,435 Brownlee Nov. 3, 1936 2,089,992 Campbell Aug. 17, 1937 2,359,543 Branzell et a1. Oct. 3, 1944 2,494,098 Lockman Jan. 10, 1950 FOREIGN PATENTS 208,551 Great Britain June 5, 1924 415,224 Great Britain Aug. 23, 1934 537,038 France May 13, 1922 

1. A METHOD OF TREATING VEGETABLE FIBER PULP WITH CHLORINE GAS IN TWO STAGES IN WHICH THE FIBER CONCENTRATION OF THE PULP IS REDUCED IN THE SECOND STAGE, CHARACTERISED IN THAT DURING THE FIRST STAGE THE REACTION WITH THE GAS IS CARRIED OUT ON THE PULP IN CONTINUOUS, UNINTERRUPTED FORM HAVING A FIBER CONCENTRATION FROM BETWEEN 10% TO 40% FOR A PERIOD OF BETWEEN 10 TO 45 MINUTES, WHEREAFTER THE PULP WITHOUT MODIFICATION PASSES DIRECTLY TO A SECOND STAGE ZONE WHERE IT IS DILUTED SO THAT ITS FIBERS CONCENTRATION IS BELOW 10% AND WHERE CONTINUED REACTION TAKES PLACE FOR A PROLONGED PERIOD UP TO ONE HOUR, AND THE METHOD BEING FURTHER CHARACTERIZED IN THAT THE QUAN- 